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Fixed bug#11753187 (formerly known as bug 44585): SP_CACHE BEHAVES AS

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MEMORY LEAK.

Background:
 - There are caches for stored functions and stored procedures (SP-cache);
 - There is no similar cache for events;
 - Triggers are cached together with TABLE objects;
 - Those SP-caches are per-session (i.e. specific to each session);
 - A stored routine is represented by a sp_head-instance internally;
 - SP-cache basically contains sp_head-objects of stored routines, which
   have been executed in a session;
 - sp_head-object is added into the SP-cache before the corresponding
   stored routine is executed;
 - SP-cache is flushed in the end of the session.

The problem was that SP-cache might grow without any limit. Although this
was not a pure memory leak (the SP-cache is flushed when session is closed),
this is still a problem, because the user might take much memory by
executing many stored routines.

The patch fixes this problem in the least-intrusive way. A soft limit
(similar to the size of table definition cache) is introduced. To represent
such limit the new runtime configuration parameter 'stored_program_cache'
is introduced. The value of this parameter is stored in the new global
variable stored_program_cache_size that used to control the size of SP-cache
to overflow. 

The parameter 'stored_program_cache' limits number of cached routines for
each thread. It has the following min/default/max values given from support:
  min = 256, default = 256, max = 512 * 1024.
Also it should be noted that this parameter limits the size of 
each cache (for stored procedures and for stored functions) separately.

The SP-cache size is checked after top-level statement is parsed.
If SP-cache size exceeds the limit specified by parameter
'stored_program_cache' then SP-cache is flushed and memory allocated for
cache objects is freed. Such approach allows to flush cache safely 
when there are dependencies among stored routines.
This commit is contained in:
Dmitry Shulga
2012-01-25 15:59:30 +06:00
parent 7bec00e131
commit d460f1689d
11 changed files with 177 additions and 0 deletions
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6
sql/sql_prepare.cc
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@ -2195,6 +2195,9 @@ void mysqld_stmt_prepare(THD *thd, const char *packet, uint packet_length)
thd->protocol= save_protocol;
sp_cache_enforce_limit(thd->sp_proc_cache, stored_program_cache_size);
sp_cache_enforce_limit(thd->sp_func_cache, stored_program_cache_size);
/* check_prepared_statemnt sends the metadata packet in case of success */
DBUG_VOID_RETURN;
}
@ -2560,6 +2563,9 @@ void mysqld_stmt_execute(THD *thd, char *packet_arg, uint packet_length)
stmt->execute_loop(&expanded_query, open_cursor, packet, packet_end);
thd->protocol= save_protocol;
sp_cache_enforce_limit(thd->sp_proc_cache, stored_program_cache_size);
sp_cache_enforce_limit(thd->sp_func_cache, stored_program_cache_size);
/* Close connection socket; for use with client testing (Bug#43560). */
DBUG_EXECUTE_IF("close_conn_after_stmt_execute", vio_close(thd->net.vio););